Commercial fire alarm systems may include fire alarm control panels networked together or networked with other fire alarm equipment including terminals or workstations. The network utilized by the fire alarm control panel may be an Ethernet network as governed by the IEEE 802.3 standard. The 802.3 standard governs the physical layer (layer 1) and media access control (MAC) of the data link layer (layer 2) in Ethernet. Devices such as data switches, hubs, and routers, provide the nodes and infrastructure of the Ethernet. The 802.3 standard requires isolation between ground and the Ethernet cabling for safety and also isolation from port to port. Intentional direct current paths to ground from the Ethernet cabling are not permitted under the 802.3 standard.
The latest revision of the Standard for Control Units and Accessories for Fire Alarm Systems (UL 864, 9th Edition) presently governs all fire alarm control panels and connected equipment. To comply with UL 864, devices used with a fire alarm control panel for control applications should be capable of reporting unintentional ground connections. Intentional paths to ground for monitoring for possible stray ground connections are acceptable.
What is needed is a ground fault detection device for use with a network device that is capable of detecting insufficient circuit impedance to ground.